A practical microbiochemical procedure for analysis of vitamin E in either solid or fluid tissues

Vitamin E distribution in ocular tissues following long-term dietary depletion and supplementation as determined by microdissection and gas chromatography-mass spectrometry

Vitamin E is thought to be important for protection of polyunsaturated fatty acids (PUFA) from oxidative damage. A microbiochemical procedure using microdissection and gas chromatography-mass spectrometry was developed to determine vitamin E distribution in ocular tissues in a rodent model, with the eventual goal of using it in a study of phototoxic degeneration of the retina, where PUFA oxidation is potentially the causal mechanism. Sample preparation was achieved by freeze-drying the retina followed by micro-dissection to obtain the desired structures for analysis. A deuterated alpha-tocopherol internal standard is added to the tissue sample before extraction and derivatization which are achieved in a single step. The data presented show the vitamin-E content in various structures of the retina, particularly the outer segments and retinal pigment epithelium (RPE); however, the vitamin E content of other ocular tissues is also included. Data were obtained from albino and pigmented rats receiving vitamin E-depleted, supplemented, and regular chow diets, and from rabbits and cats receiving regular chow diets formulated for each species. Within all dietary groups the highest concentration of vitamin E was located in the RPE followed by the outer segments of the photoreceptor cells. Other ocular tissues consistently contained lower amounts of vitamin E. Different tissues were depleted of vitamin E at different rates and this points out the importance of determining vitamin E levels in tissues of interest in studies on the consequences of dietary depletion.

Occurrence of 4-hydroxyalkenals in rat tissues determined as pentafluorobenzyl oxime derivatives by gas chromatography-mass spectrometry

Malondialdehyde measurements have been the major tool for studying relationships between lipid peroxidation and tissue pathology. Recently, we presented a novel gas chromatography-mass spectrometry method for direct detection of phospholipid peroxides with picogram sensitivity based on transesterification of phospholipids or triglycerides to form pentafluorobenzyl esters. Under some circumstances the reactive primary oxidation products break down. Therefore, we developed a convenient, high sensitivity method to detect more stable secondary lipid oxidation products, the 4-hydroxyalkenals. The method accomplishes a facile extraction of 4-hydroxynonenal from tissues by forming pentafluorobenzyl oxime derivatives to displace aldehydes from Schiff base linkages. 4-hydroxynonenal was found in heart, liver, adrenal, and testis from rats and was detected to the 10-100 pg level by the current method.

Gas chromatography-mass spectrometry method for determination of phospholipid peroxides; I. Transesterification to form methyl esters

The purpose of this study is to develop methods for determining the chemical species of lipid peroxides that occur in various types of tissue pathology. Experiments are aimed at determining the phospholipid peroxides associated with retinal degeneration as the initial test case. Phospholipid hydroperoxides are synthesized by photosensitized oxidation, chemically characterized and used to develop an effective and simplified method to identify and measure phospholipid hydroperoxides by gas chromatography-mass spectrometry (GC-MS). A sensitive reverse phase high performance liquid chromatography (HPLC) method is also presented to separate peroxidized phospholipids from phospholipids. For GC-MS, phospholipid peroxides are reduced with sodium borohydride and transesterified to form fatty acid methyl esters using a mild quaternary ammonium hydroxide catalyst. The hydroxyl groups produced by reducing the hydroperoxides are formed into trimethylsilyl ethers and GC-MS is employed (with electron ionization and negative ion chemical ionization) to identify oxidized fatty acids at the 10 ng level. Photooxidation of (palmitoyl)(linoleoyl) phosphatidylcholine yielded equal amounts of the conjugated (9 and 13 isomers) and the nonconjugated (10 and 12 isomers) linoleoyl hydroperoxides. Photooxidation of rat retina total lipids yielded oxidation products of oleolyl (18:1) esters as well as the conjugated and nonconjugated oxidation products of arachidonoyl (20:4) and docosahexaenoyl (22:6) esters virtually all of which arise from phospholipids. The nonconjugated products are of interest as indicators of photosensitized light damage in retina and other tissues. It is notable that all the possible singly oxidized products are found with the exception of the 4, 5 and 7 hydroperoxides of 22:6 and the 5 hydroperoxide of 20:4. It appears that the approach of singlet oxygen is strongly inhibited in the sterically hindered region near the phospholipid head groups.